End loaded planar spiral antenna



March 15, 1956 'm1, LEQHTREQK 3,241,148

END LOADED PLANR SPIRAL ANTENNA Filed April 4, 1960 IO/ l2 F|G.2. 22

INVENToR.

LAWRENCE w. I ECHTRECK ATTORNEYS United States Patent O 3,241,148 END LOADED PLANAR SPIRAL ANTENNA Lawrence W. Lechtreclr, St. Louis County, Mo., assignor to McDonnell Aircraft Corporation, St. Louis, Mo., a corporation of Maryland Filed Apr. 4, 1960, Ser. No. 19,850 3 Claims. (Cl. 343-895) The present invention relates to antennas in general and more particularly to broad band antennas.

It is well known to construct broad band antennas by interwinding the elements thereof. It is also well known that broad band characteristics can be achieved by interwinding the elements of an antenna in a spiral, however, the known constructions are relatively large and bulky requiring considerable space for mounting, and the known constructions are also relatively inefficient to operate and require separate means apart from the antenna itself for matching the antenna to an associated unit of equip ment such as a radar set or lthe like. Furthermore, the known devices Iare relatively complicated to construct and are relatively vulnerable to damage caused by jarring and vibration. These and other disadvantages of the known devices are overcome -by the present invention.

Briefly, the present antenna comprises a pair of spirally interwound, spaced and coplanar elements one of which has a portion integral therewith for loading the antenna and the other of which has a connection to ground and also a coaxial cable mounted thereon, said cable having one conductor which makes connection with said associated element and another conductor which makes connection with the other element at a central location on the antenna.

It is a principal object of the present invention to provide an antenna having broad band characteristics and small electrical size achieved through end loading.

Another object i-s to provide simple means for loading antennas.

Another object is to provide an inexpensive, compact, and eicient broad band antenna construction.

Another object is to reduce the size and weight of antenna devices.

Another object is to reduce the number of antennas required to cover a frequency range.

Still another object is to reduce the size and weight of air and space borne equipment.

These and other objects and advantages of the present invention will become apparent after reading the following detailed specification in conjunction with the accompanying drawing, wherein:

FIG. 1 is a plan View of an antenna device constructed according to the teaching of the present invention, and said view being -in the plane of the antenna, and

FIG. 2 is a cross sectional view taken on line 2 2 of FIG. 1.

In the drawing, the number refers generally to an antenna constructed according to lthe present invention. The antenna 10 is constructed of two spaced and mutually insulated interwound elements 12 and 14. The elements 12 and 14 may be formed of flat relatively thin metal, such as copper, and mounted on an insulator, such as the insulator 15; they may be formed by etching a copper surface applied to a dielectric element, such as the insulator 15; they may be suspended in air; or they may be formed in any other suitable way.

The most important characteristics of the elements 12 and 14 are that they be formed of electrical conductive material, that they be positioned substantially in one plane, that they be spaced and mutually insulated from each other, that they have approximately, although not necessauily, the same overall length, that the element 12 Patented Mar. 15, 1966 ICC be connected to a conducting ground plane, and that the element 14 be end loaded by a portion 24.

A coaxial cable 16 is shown mounted centrally on the element 12 and extends substantially the full length thereof. It is contemplated, however, that the cable 16 could be positioned in other locations on the associated element 12. In the embodiment shown in the drawing, the cable 16 has an outer conductor 18 which is soldered on the surface of the element 12 and an inner conductor 20 (insulated from Ithe outer conductor 18) which extends across the gap 22 between the innermost ends of the elements `12 and 14, said inner conductor being connected to the element 14. The opposite end of the conductor 20 is connected to a suitable device such as a radar set, a radio receiver, a transmitter, or other similar type of device, not shown.

In the particular embodiment of the antenna shown, the outer conductor 18 of the coaxial cable 16 and the associated element 12 are grounded electrically and the outer end of the element 14 is formed integral with a portion 24. The size and shape of the portion 24 is varied depending upon the characteristics of the antenna and its connection to the ground plane 26. The port-ion 24 i-s provided to load the antenna and to provide proper match for eflicient operation particularly at the lower part of its frequency band where ordinary spirals cannot perform.

The size and shape of portion 24 are determined empirically since it depends on the desired lower cutoff frequency and the structure adjacent to the antenna. The existence of end loading 24 and grounding at 26 allow the use of antennas whose largest dimension are less than of IAS the longest radiated wave length. Frequency band widths as large as 30:1 have been obtained through end loading and grounding.

The impedance ofthe antenna 10 is determined by the metal to gap ratio of the spiral and also by the size of the portion 24. The metal to gap ratio also effects the size of the portion 24.

The shapes and spacing of the antenna arms and the shape and size of the end-loading portion 24 also have an effect on the operating characteristics and, of course, can be varied as aforesaid to produce a particular operating condition.

In actual practice it has been found that the antenna 10 can have overall dimensions that are substantially smaller than other known antennas having similar broad band characteristics. This is an important feature of the present device especially when used on air borne and space borne vehicles where weight and space requirements are Very restricted.

Thus, it is apparent that there has been provided a novel antenna device which fulfills all of the objects and advantages sought therefor. Obviously, many of the specic characteristics of the present antenna, as shown, could be changed, altered or modified by those Iskilled in the art without departing from the spirit and scope of the invention. All such changes, alterations and modifications which do not depart from the spirit and scope of the invention are deemed to be covered by the present invention which is limited only by the claims which follow.

What is claimed is:

1. An antenna comprising a pair of spirally interwound, spaced and coplanar elements, one of which has a portion formed integral therewith at one end for end loading and matching the antenna, means connecting the other of said elements to ground, and `a coaxial cable mounted on said other element, said cable having two conductors, each of which are connected to a different one of Said elements.

2. An antenna comprising a pair of mutually insulated spiral shaped elements interwound in spaced and CO- planar relation about a central location, said elements being relatively flat and thin in the plane of the antenna, means grounding one end of one of said elements, the other of said elements having an enlarged coplanar portion formed integral with one end thereof for loading the antenna, said enlarged portion being of a size to provide a proper match for efficient operation at relatively low frequencies, and a transmission line connected to the antenna, said transmission line including a pair of spaced conductors each of which is connected to a different one of said elements.

3. An antenna comprising two mutually insulated, metallic, spiral shaped strips interwound with each other and supported in the same plane, the Width of said strips and the spacing therebetween varying along the lengths thereof, one of said strips having an enlarged coplanar end portion integral therewith and of determinable area size for loading the antenna, and means connecting the other of said strips to a ground plane.

References Cited by the Examiner UNITED STATES PATENTS 2,083,260 6/1937 Godley et al. 343-792.5

4 2,485,930 10/1949 Silliman 343-863 X 2,856,605 10/1958 Jacobsen 343-895 X 2,863,145 12/1958 Turner 343-895 X 2,875,443 2/1959 Kandoian 343-752 X 2,935,746 5/1960 Marston et al. 343-895 X 2,958,081 10/1960 Dyson 343-908 X 3,015,101 12/1961 Turner et al. 343-895 X 3,034,121 5/1962 Riblet 343-895 X 3,083,364 3/1963 Scheldorf 343-895 X 3,135,960 6/1964 Kaiser 343-895 X OTHER REFERENCES Aviation Week, July 1958, vol. 69, No. 2, TL-SOI-AS, pps. 75, 77, 79, 81, 82.

Published I, Isbell, Proceedings of the IRE, vol. 47,

0 No. 6, June 1959, page 1152 relied on.

ELI LIEBERMAN, Acting Primary Examiner.

GEORGE N. WESTBY, HERMAN KARL SAALBACH,

Examiners. 

1. AN ANTENNA COMPRISING A PAIR OF SPIRALLY INTERWOUND, SPACED AND COPLANAR ELEMENTS, ONE OF WHICH HAS A PORTION FORMED INTEGRAL THEREWITH AT ONE END FOR END LOADING AND MATCHING THE ANTENNA, MEANS CONNECTING THE OTHER OF SAID ELEMENTS TO GROUND, AND A COAXIAL CABLE MOUNTED ON SAID OTHER ELEMENT, SAID CABLE HAVING TWO CONDUCTORS, EACH OF WHICH ARE CONNECTED TO A DIFFERENT ONE OF SAID ELEMENTS. 